Recently, research is being actively conducted on a UWB communication that coexists with the existing wireless communication service without securing a separate frequency resource and enables a wireless communication using a high-speed wide band.
The UWB communication, which transmits data using very short pulses of several nano seconds, has several features different from the existing narrow band communication. The UWB communication fundamentally transmits a signal using a pulse, and thus has a wide frequency band and a low transmission power density. Since the UWB communication uses a wide bandwidth and has relatively low power consumption, the UWB communication can transmit data at a high speed, perform multiple accesses, and perform a communication even in a band less than a noise band. However, the UWB communication may collide with the service band of a different wireless communication network due to the use of the wide bandwidth. Therefore, each country defines the limit of an emission power of the UWB communication so as not to interfere with the existing channels. In other words, each country has licensed the UWB communication service on the assumption that the service band of the UWB communication interfering with that of a specific wireless communication maintains power to less than reference power.
For example, in order to protect the existing communication system and a communication system that may be introduced in the future, some countries, e.g., Europe, Japan, China, and Korea other than the USA regulate a technology reference that needs to detect the other communication signal having a certain level and take a measure for protecting the other communication system using the detected communication signal for the purpose of using the UWB system in a specific frequency band.
To date, a definite global common reference has not been determined for the kind of a victim signal and a victim signal detection level for applying an avoidance technology reference that is being discussed for allowing the MB-OFDM (Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band) UWB communication in a band of 3.1 GHz to 4.8 GHz, and the victim signal detection level for applying DAA (Detection And Avoidance) technology to a UWB communication system or a victim communication system to be protected is being established according to the condition of each country. Also, a DAA technology reference is being discussed mainly on the setting of the victim signal detection level for protecting a victim signal and the avoidance algorithm that is applicable according to the victim signal detection level.
FIG. 1 exemplarily shows a subcarrier interval and a victim signal position of a narrow band disposed within the subcarrier interval in the 128 FFT window of an MB-OFDM UWB system. Particularly, in FIG. 1, the victim signal has an occupied bandwidth narrower than the subcarrier interval of a Fast Fourier Transform (FFT) module of an MB-OFDM UWB receiver, of which the occupied bandwidth is 1.75 MHz and a frequency offset is 80 MHz. A subcarrier interval of MB-OFDM is 4.125 MHz, and thus, when the frequency bandwidth of a victim signal to be detected is 1.75 MHz and a center frequency is 80 MHz, the victim signal is disposed between 79.125 MHz and 80.875 MHz. In this case, in FFT of MB-OFDM UWB, the position of a subcarrier number 19 is 78.375 MHz, the position of a subcarrier number 20 is 82.5 MHz, and the position of a subcarrier number 21 is 86.625 MHz. As such, a victim signal is disposed between the subcarrier number 19 and the subcarrier number 20 and thus is not detected in an MB-FFT result well.
FIG. 2 shows a detection result of a victim signal of a narrow band using the 128 FFT of an MB-OFDM UWB receiver. Particularly, FIG. 2 is an output result when a detection algorithm using FFT has been driven for a received victim signal as in FIG. 1. In FIG. 2, reference numeral 200 indicates a victim signal detection reference line. As known from FIG. 2, a victim signal having a frequency bandwidth narrower than a subcarrier interval is shown as not normally being detected.
As described above, when the frequency bandwidth of a victim signal such as a WiMAX (World Interoperability for Microwave Access) signal is narrower than a subcarrier frequency bandwidth used in the MB-OFDM UWB receiver, the MB-OFDM UWB receiver cannot accurately detect the victim signal disposed within a subcarrier interval to date.